PVC "glue" is not really glue. It is a chemical that welds the fitting/pipe so it can not be unglued. One way you can avoid tearing out everything is to just cut out the bad section, leaving pipe stubs. The use a Fernco coupler to connect new pipe/fittings. This is a neophrene sleeve with stainless steel clamps on each end. It will allow some flex if the pipes don't match perfectly (get as close as possible, there is a limit)